CXCR4 and neoplasm: Increased CXCL12 expression in hypoxic tissues is important for the homing of tumor stem cells in circulating tissues (112), CAFs secrete CXCL12, attract CXCR4-expressing tumor cells and endothelial progenitor cells, thereby promoting angiogenesis in the liver’s pre-metastatic niche (113, 114).